1. Field of the Invention
This invention relates generally to dilation catheters. More particularly, this invention relates to intravascular catheter balloons.
2. Previous Art
Various dilation catheters rely upon an inflatable balloon for applying pressure against the interior of a biological conduit such as a blood vessel. These inflatable balloons come in various shapes and sizes to perform any of a number of functions. For example, dilation catheters are used in percutaneous transluminal coronary angioplasty (PTCA); vascular prosthesis implantation; atherectomy and various other medical procedures.
In classical PTCA, a hollow guiding catheter, a guidewire and a dilation catheter are inserted into the vasculature of a patient. The guiding catheter has a pre-shaped distal tip which is percutaneously introduced into the vasculature and advanced. An operator, such as a surgeon, twists and moves the proximal end of the guiding catheter to advance the distal tip through the aorta. The distal tip reaches the ostium of a diseased coronary artery. An example of a guiding catheter and the operation thereof is disclosed in U.S. Pat. No. 5,348,545 (Shani et al), the disclosure of which is incorporated herein by reference.
While the distal end of the guiding catheter is seated in the ostium, the guidewire advances out the distal tip of the guiding catheter into the diseased coronary artery. The operator twists the proximal end of the guidewire to guide the curved distal end of the guidewire. The operator advances the guidewire within the coronary anatomy until the shaped distal end of the guidewire enters the diseased coronary artery. The diseased artery may include a stenosed region having a lesion, for example. This advancement of the guidewire continues until the guidewire crosses a lesion, prosthetic implant or other region to be dilated.
The dilation catheter slides over the guidewire and through the guiding catheter. The dilation catheter then advances out of the distal tip of the guiding catheter, over the previously advanced guidewire until the balloon on the distal end of the dilation catheter is properly positioned adjacent to the lesion.
Fluid inflates the balloon to a predetermined size. The fluid often pressurizes the balloon at pressures which may reach 20 atm but which are often within the range of 4-12 atm. Conventional balloon designs have two ends attached to the catheter, a working length and a tapered portion. The tapered portion extends between the balloon end and the working length. Accordingly, the tapered portion defines a transition between the shaft and the balloon end and the working length.
The angle at which tapered portion extends from the catheter is typically greater than 200. The length of the taper (taper length) is typically less than 3 mm.
A variety of dilation catheters exist which may have different purposes including prosthetic implantation, angioplasty, atherectomy, diagnostic procedures and even various re-vascularization techniques which are being developed. Rapid exchange and over the wire types of dilation catheters are two common types of dilation catheters. Examples of various dilation catheters having a balloon are disclosed in U.S. Pat. No. 4,582,181 (Samson); U.S. Pat. No. 5,350,395 (Yock); U.S. Pat. No. 5,242,399 (Lau et al.); U.S. Pat. No. 5,334,154 (Samson et al.) and U.S. Pat. No. 5,480,383 (Bagaoisan et al). The disclosures of these patents are incorporated herein by reference.
Multiple lesions may exist in a diseased coronary artery. It is desirable to move the deflated balloon across any number of these lesions to optimally position the balloon within the artery for inflation against a selected lesion. With known balloon designs the deflated balloon may experience considerable frictional force between the balloon and the lesion when the balloon crosses the lesion. These are known as cross forces. During withdrawal of the balloon, the balloon may similarly experiences such frictional forces across the lesion. These forces are known as recross forces. Cross and recross forces are sought to be minimized.
Cross and recross forces may inhibit smooth movement of the deflated balloon within the vasculature of a patient, cause thrombus buildup, and may be uncomfortable to the patient. Additionally, if the patent has a stent located near the crossed or recrossed lesion, the cross and recross forces may dislodge the stent. Given that stent implantation is becoming more common, ways to avoid stent dislodgment are increasingly important considerations for balloon designers.
What is desired is an improved balloon design which more easily crosses lesions while the balloon is deflated. What is also desired is an improved balloon which reduces cross and recross forces.